Well-known are electric drives of end-face rotor-stator interaction type, where the rotor is a disk, on the end surfaces whereof permanent magnets of alternating polarity are located over the circumference. The stator of such machines is made in the shape of a disk (ring), installed coaxially with the rotor thus the stator and the rotor located in different planes, electromagnetic stator coils being located at the end faces of the stator. For instance, the direct current brushless electric motor (electric drive) described in U.S. Pat. No. 5,440,185 “Composite Magnet Brushless DC Motor” belongs to this type of electric machines. The known device includes at least one rotor installed on the axle and made as a multi-pole magnetic disk consisting of sections spaced along the circumference, where the polarity of the sections alternates. The device also includes at least one disk-shaped stator element, determining the rotor position, the device for mounting the rotor (rotors) and stator element (elements) on the common axle, the sensor for positioning the multi-pole magnetic disk versus the stator element and a device to identify the magnetic field profile in the stator elements. Two windings are wound over the stator elements, electric current being fed to one of those thus determining the polarity of the stator poles. The known device is not easy in manufacturing, the biggest difficulty being manufacturing of disk-shaped rotors with magnetic poles of alternating polarity.
The improved design described in U.S. Pat. No. 6,515,390 “Electric Drive” and comprises a rotor made in the form of two disks, the teeth of which on the outer or inner circumference make up rotor poles and an axially magnetized polygon or cylindrical magnet placed between said disks. The stator made in the form of coils that are distributed over the circumference and that are installed predominantly in the space between the rotor poles provides for the possibility of the end face interaction with the rotor poles. The rotor could be made as a multi-sectional unit. In this case the disks have the plate-like shape, and the poles of one disk are coincided with the poles of another disk in one plane, while the magnets of adjacent section are oriented towards one another with like poles. The disks could be made integral with a magnet in such a manner that they serve as magnet's poles. The rotor poles are located in the planes perpendicular to device axis and stator poles are located in such a way that a possibility of the end face interaction with rotor poles is provided for, it becomes possible to reduce the radial size of the device. A plate-like shape of said disks makes it possible to optimize the size of the device depending on the magnet and stator used required power and the size of a device, in which this electric drive is supposed to be mounted.
The known flat brushless DC electric drives are often using with blowers for electronic cooling systems, for instance U.S. Pat. No. 6,664,673 “Cooler for electronic devices”. The regulation of the temperature due to heat generated inside the housing of an electronic device is an important consideration during the design of an electronic device. Cooling is important because if left unchecked, heat can cause electronic devices to malfunction during use or lead to premature device failure. As improvements in processor size and speed occur, the amount of heat generated by the larger and faster processors also increases. Additionally, improved processors require larger power supplies and auxiliary components that generate increased amounts of heat and require improved systems for heat removal.
Another factor that aggravates the need for improved heat removal cooling systems is the trend towards making computing devices smaller and especially thinner. The trend toward smaller and thinner electronic devices having larger, faster processors renders the traditional heat removal cooling systems inadequate for several reasons.
In order to enhance the cooling capacity of a cooling device, an electrically powered blower is often mounted within or on top of a heatsink of the cooling device. In operation, the blower forces air to pass over fins of the heatsink, thus, cooling the heatsink by enhancing the heat transfer from the fins into the ambient air.
According to mention above modern requirements for cooling devices especial importance is devoted to electric drives used with blowers. Thus, modern electric drive must have high efficiency, enough torque, low noise generation and compact size.
Due to modern requirements for cooling devices, especially in respect to a combination of the thermal efficiency and an available space, flat electric drives are often used with radial type impellers of blowers for cooling of electronic components. There are such devices describe in U.S. Pat. No. 6,664,673 “Cooler for Electronic Devices” and No. 6,700,781 “Heat-Dissipating Module for Removing Heat Generated from Heat-Generating Device”. Also, an invention described in U.S. Pat. No. 6,698,505 “Cooler for electronic device” discloses a crossflow blower with a radial impeller. All mentioned above inventions comprise a flat stator plate made as circuit board and a magnetized rotor fixed to a radial impeller of the blower. The flat stator and the magnetized rotor are located in two different parallel planes and separated by an air gap.
However, such arrangement cause a vibration of the flat stator and magnetized rotor due to a rise of oscillation forces in a direction perpendicular to the planes of the flat stator and the magnetized rotor. These forces determine by an interaction between magnetic poles of the stator and rotor. In one's turn the vibration generates an increasing sound level thus contradicts with modern requirements for cooling devices.
On the other hand mentioned vibration causes energy losses thus decrease the motor efficiency of the electric drive and, correspondingly, blower efficiency.
There is an electric drive described in U.S. Provisional Patent Application No. 60/586,128 “An Integrated Blower for Cooling device” comprises a flat stator and a magnetized rotor that are located in one plane.
Although mentioned arrangement of the flat stator and the magnetized rotor solve above mentioned problems related to efficiency and a noise generation, there is another problem rising. According to this design the magnetized rotor comprising circumferential magnetic means with alternative polarities placed and magnetized along the plane of the flat stator. It is very difficult to manufacture the magnetized rotor as a whole due to problems arising during magnetization. And more, strong magnetic forces arising after magnetization lead to significant stresses that made the magnetized rotor more fragile. Therefore, such designs cannot be thin enough and manufacturing of magnetized rotor become complicate and expensive.
Above mentioned problem was solved according to U.S. Provisional Patent Application No. 60/627,405 “Flat Electric Drive” comprises a flat stator and a magnetized rotor made like a flat toothed ring. The flat stator located at a plane of the flat toothed ring and comprises at least one set of even number of circumferential arrayed alternated polarity coils with magnetic axes coincide with the plane of the ring. The flat toothed ring comprises teeth located at least one of an outer and an inner diameters of the ring, thus a number of teeth located at the same diameter is equal a half of number of the coils. The toothed ring is magnetized along radial directions thus the teeth located at the same diameter are like poles.
Both last mentioned electric drives comprise spatial coils wound around the core, thus a production of such stators is complicate and expensive.
It would be desirable to provide a compact flat electric drive and a method of manufacturing the same that would overcome these aggregate problems associated with simplicity, cost, efficiency, torque and sound level.